Microwave electron discharge device



Aug. 16, 1955 s. E. WEBBER MICROWAVE ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed Feb. 27, 1951 ig. I.

Inventor: Stanley El. Webber,

by w w His Atcovney.

Aug. 16, 1955 Filed Feb. 27, 1951 s. E. WEBBER 2,715,697

MICROWAVE ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 2 Inventor:

Stan I ey E1. Webber,

His Attorney.

United States Patent O MICROWAVE ELECTRON DISCHARGE DEVICE Stanley E. Webber, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 27, 1951, Serial No. 212,939

19 Claims. (Cl. 315-39) This invention relates to improvements in microwave apparatus, and has for an object the provision of improved apparatus for generating or amplifying electromagnetic waves having a frequency in the order of three hundred thousand megacycles. Other objects and advantages will appear as the description proceeds.

It is known that under certain conditions an electromagnetic wave transmitted in proximity to a high velocity electron beam can absorb energy from the beam. In previous devices utilizing this principle for the generation or amplification of microwaves, an important limitation has been that electrons must be accelerated to high velocities, requiring high accelerating voltages. In the present invention, this difficulty is avoided by using the cyclotron principle, by which electrons are accelerated to very high velocities by repeated passage across accelerating gaps driven by a relatively small alternating voltage. in this way, electrons may be accelerated relatively easily up to exceedingly high velocities in the order of one-half the velocity of light. These high velocity electrons transfer energy to an electromagnetic wave transmitted at nearly the same velocity through a wave guide structure arranged about the periphery of the electron orbits.

It has previously been proposed that electrons accelerated through the cyclotron principle may be used to generate electromagnetic waves by their action upon resonant, oscillatory structures. In the present invention, such oscillatory structures are not essential, since the beam interacts with a continuously moving wave transmitted at a velocity near that of the electrons.

The features of this invention which are believed to be novel and patentable are pointed out in the claims which form a part of this specification. For a better understanding of the invention, reference is made in the following description to the accompanying drawings, in

which Fig. 1 is a horizontal section of improved microwave apparatus, Fig. 2 is a vertical section of the same apparatus, Fig. 3 is a schematic horizontal section of a modification, Fig. 4 is a schematic perspective view, partly in section, of other improved microwave apparatus, and

Fig. 5 is a schematic vertical section of other improved microwave apparatus.

Referring now to Figs. 1 and 2, an evacuated structure comprises an envelope or case 1 and a pair of hollow electrodes 2 and 3. Each of the electrodes 2 and 3 contains a substantially semi-circular hollow portion, so that together they form a substantially circular hollow space 4, as shown. Within this circular hollow space is an electron-emitting cathode 5, which may be a small metal filament connected at one end to a lead 6 and connected at its other end to case 1 through electrode 3. Voltage applied between case 1 and lead 6 in the conventional manner causes current to flow through filament 5, which heats the filament sufliciently for thermionic emission of electrons. Means such as a magnet having pole pieces 7 and 8 produces a magnetic field through space 4 which causes elec- "ice trons emitted by cathode 5 to travel in orbital paths about the cathode, as represented by dotted lines 9.

Electrodes 2 and 3 are separated by an accelerating gap 10, across which an accelerating voltage is provided as hereinafter explained. The electrons traveling in orbital paths about the cathode repeatedly traverse gap 10, and at each crossing are accelerated so that the electrons gain velocity and travel in orbits of increasing radius until they strike electrode 2 or electrode 3. Electrons in the a, outer orbits travel at exceedingly high velocities, which may be in the order of one-half the velocity of light.

it is know that electrons traveling in orbital paths of the type described, having linear velocities below that at which the relativistic increase in mass becomes significant, travel at a constant angular velocity determined solely by the strength of the magnetic field, regardless of the linear velocity of the electrons. The relativistic increase in mass at very high linear velocities limits the maximum electron velocities obtainable with this arrangement to about one-half the velocity of light. Accordingly, the electrons may be accelerated up to a velocity of about one-half the velocity of light by an alternating voltage applied across the accelerating gap 10 in synchronism with the period of angular rotation of the electrons. Preferably, this alternating voltage is supplied by electromagnetic waves within a resonant cavity 11 to which the electromagnetic energy is supplied, through a probe 12 and a coaxial connection 13, from any suitable source. A similar resonant cavity 14 may be provided at the other end of the gap 10, as shown, for better excitation of the gap. Cavity 14 is excited by the voltage across the gap, and hence requires no external excitation.

An annular wave guide 15 extends around the outside of circular space 4, and hence about the periphery of the electron orbits. As is known, the phase or wave velocity of electromagnetic waves transmitted by a wave guide is greater than the velocity of light, especially at frequencies near the cut-off frequency of the wave guide. However, since the radius of the wave guide is greater than the radii of the electron orbits, the electromagnetic waves transmitted by the wave guide may have nearly the same angular velocity as the electrons, although they have much larger linear velocities. The proportions of wave guide 15 are such that the angular velocity of electromagnetic waves transmitted, of the frequency which is desired to generate or amplify, is near and slightly less than the angular velocity of electrons in the outermost orbit. Interaction between the waves transmitted by wave guide 15 and the electrons in the outermost orbits occurs through a plurality of slots 16, or other suitable coupling means, in the inner wall of the wave guide. In this inter-action, energy is transferred from the electrons to the electr0- magnetic waves, so that the waves are amplified and increase in amplitude. In this way, electromagnetic waves of substantial amplitude are quickly built up within wave guide 15. These amplified Waves are necessarily of the desired frequency, since waves of other frequencies are transmitted by the wave guide at different velocities, and only those waves traveling at angular velocities near the velocity of the electrons inter-act with the electrons and receive energy therefrom. Slots 16 also serve the purpose of reducing somewhat the velocity of waves in the waveguide, and thus assist in matching the wave velocity to the electron velocities.

Since any random disturbance may initiate an electromagnetic wave which will be amplified and quickly built up to a substantial amplitude, the device described is inherently an oscillator at a frequency determined by the wave guide dimensions and the velocity of the fully accelerated electrons in the outermost electron orbits. This frequency can be adjusted, within limits, by adjusting the electron velocities, by simultaneously adjusting the lations in wave guide 15, and thereby signal to a negligible value.

' of.-the outermost electron orbits, s

1 7 wave in the wave guide.

strength of themagnetic field and the frequency of the 'driving voltage .across gap 10. To utilize these oscilla .tions, a portion of the electromagnetic wave within wave guide 15 maybe transmitted through a slot 17, or other suitable coupling means, in the outer Wall of a wave guide I'to' a resonant chamber'18, and thence'through a convenmay be connected to electrode 3 6, 'asshown, to aid the tional resonant window 19 in the wall of envelope 1 to an .output connection20. The output will be highest when 'the output frequency is an integral multiple of the input frequency... The. device may be used asan amplifier if the-inherent tendency of the apparatus to oscillate is suppressed. This mayibe done by placing an attenuator 21"at a suitable location Within' wave guide 15. Attenuator 21 may be a small pad of lossyrnaterial which absorbs enough energy from electromagnetic waves within the waveguide I to'prevent random disturbances from building up to sub-' s'tantial amplitude. Input signals may then be fed into 1 the wave guide through an input connection 22, a resonant window 23, a'resonant chamber24 and'a slot25."When' 2 input signals are fed'into the wave guide 15, these sig nals travel around the wave guide and are amplified by inter-action with the electrons in circular space 4, thereby I producing oscillations of larger amplitude at output conncctiori 20. i In the absence of an input signal, attenuator 21 absorbs sufiicient energy to prevent substantial oscilreduces the output Fig. 3 shows a'modification especially useful as an oscillator; .In thjs figure, two hollow electrodes 26 and27, separated by an accelerating gap 28, form a substantially circular space '29. Within space 29 is a source of electrons, suchas electron-emitting cathode 30. Accelerating voltage 'is'provided across gap 28 by any suitable means 3 31.: -A suitable envelope'or ca'se,-not shown, is provided f to keep space 29-evacuated, and' a magnetic field 'isp'rovided through space 29 by suitable means, not shown, such I Apluralityof small' res'onant cavities 32 are arranged 'garo und the periphery of the electron orbits, as shown. These' cavities areconnected to an annular wave guide 33 through a plurality of slots 34,"or other suitable means.

I output. connection from the wave' guide isprovided at 35. 5 V Inthe operation-of this modification, the accelerated electrons supply energy to maintain electromagnetic oscillations'in each of the small'resonant cavities 32. These oscillations supply energy through slots '34 to maintain a traveling" electromagnetic wave in wave guide 33. The radius'of wave guide 33is approximately twice the radius 0 that waves traveling initial acceleration of electrons across the gap..

Around the'periphery of the electron orbits is a wave guide structure comprising a ring 42 of dielectric material. Since this ring of dielectric material is a good electrical insulator, it may extend continuously across gap 38 withthe'electron orbit space, and thus inter-acts with the ace ceieratecl electrons so that the'electrons transfer energy to the electromagnetic wave and amplify any'randomdisturbance to a wave ofsubstantial amplitude traveling around the annular wave guide. A portion of'this amplified wave may be utilized through an output connection43 coupled tothe wave guide in any suitable manner, for example, by an additional piece of dielectric material attached to ring 42.

'Since the. apparatus has an inherent tendency to" oscillate at a frequency determined by the electron velocities and the characteristics ofthe wave guide, it is'especially useful as a generator of electromagnetic waves having very short wave lengths. For use as an amplifier, an input connection is provided at'the other side of the annular j as-a magnet. Theelectrons travel in orbital paths about cathode 30, and are accelerated to high velocities "by repeatedly traversing gap 28.

wave guide, similar to output connection 43, and an attenuator pad oflossy material is attached to thefwave guide at a suitable location to absorb suificient energy from the electromagnetic wave to suppress the inherent V tendency of the apparatus to oscillate. v

To prevent the accumulation of undesiredcharges fromelectrons striking the innerfsurface io f ring 42, i1a

very thin layer 44 of. electrically conducting material is'coated on' the inner surface of the dielectric ring, as shown.

a are just sufl'icient to prevent the accumulation of charges in -theiwave guide at greater than the speed of 'light have an angular velocity nearly equal to that of electrons in theoutermosti electron orbit traveling at a linear velocity.

of one-half the-speedof light. Since the 'angular velocities-are nearly equal, the proper relationship existsf for the transferof energy from the electrons to the traveling Fig. 4 shows an 'improved microwave apparatus useful for generating or amplifying waves of very. short wave length. In thisjfigure,'twouhollow electrodes 36 and 37 separated by an accelerating gap 38 form a substantially circular 'space 39. 7 Within space39 is. asource of elecfrbns,.,such" as electron-emitting cathode 40. I A suitable caseor envelope, not shown, is providedto keep space 39,evacuated, and a magnetic field isprovided through space 39. by suitable means, not shown, such-as a magnet. Theielectrons travel in orbitalpaths about the cathode, and are accelerated tohigh velocities, to one-half the velocity of light, for example, by repeatedly traversing ,gap 38,.across which an alternating accelerating voltage is;providedby any suitable means, not shown. Wires 41 on the inside of the dielectric ring, and are not suf.-, ficient to prevent the penetration of electromagnetic waves'from'the'wave guide into the region of ,theelec: tron orbits. If desired, a collector. electrode 45,. which maybe a small strip of metal positioned just inside of ring 42, may be provided to remove electrons rmm the outermost orbit before'they strike the dielectric ring. It may be noted that this form of the apparatus' hasa very simple,'sturdy and economical structure} 'Refer now to Fig. 5, which illustrates anotherf improved microwave apparatus Two hollow electrodes 4 46 and 47, separated by an accelerating gap 48, form] a substantially circular space 49. Withirrt'his space 1 there is an electron-emitting cathode "50. 'A suitable 7 case or envelope, not shown, is provided to keep space' 49 evacuated, and a'magneti'cv field is provided through space..49 by suitable means," not shown, such asia magnet. ,The electrons travel in orbital paths about cathode 50, and are accelerated to highvelocities by, repeatedly traversing gap 48, across which an accelerating voltage'is provided by suitable means, not shown.

Around the periphery of theelectron orbits is a wave guide structure comprising an annularhelix 51.-- Helix 51 is proportioned to ,transmit electromagnetic ==waves at a-velocity near that of the fully accelerated -elec trons in the outermost electron orbits, This Waveace quires energy from the electrons in the manner. herein'-,

before described, and thereby is amplified Aportion of this amplified wave may be supplied to an output connec-f t'ion 52 through a probe '53. For use as anamplifien an input connection (not shown) is provided atthe otherv side of the helix, anda suitable attenuatoris coupled At a particular 7 The thickness and conductivity of film .44 V

5 to the helix to suppress the inherent tendency of the apparatus to oscillate.

Having described the principle of this invention in the best modes in which I have contemplated employing that principle, I wish it to be understood that the examples described are illustrative only, and that other means may be employed without departing from the true scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Microwave apparatus comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, and a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully accelerated electrons.

2. Microwave apparatus comprising structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to substantially one-half the velocity of light, and a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully accelerated electrons.

3. A microwave oscillator comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully accelerated electrons, whereby such waves gain energy from the electrons and any random disturbance is quickly built up to electromagnetic waves of substantial amplitude, and an output connection coupled to said wave guide for utilizing a portion of said amplified waves.

4. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully accelerated electrons, an input connection coupled to said wave guide for supplying electromagnetic waves to the wave guide, which waves travel around the wave guide and receive energy through inter-action with the accelerated electrons, whereby the electromagnetic waves are amplified, and an output connecan evacuated 6 tion coupled to said wave guide for utilizing a portion of the amplified waves.

5. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electronemitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully accelerated electrons, an input connection coupled to said wave guide for transmitting thereto electromagnetic waves which travel around the wave guide and absorb energy by inter-acting with the accelerated electrons, whereby the electromagnetic waves are amplified, an output connection coupled to said wave guide for utilizing a portion of said amplified waves, and an attenuator coupled to said Wave guide for suppressing the inherent tendency of the apparatus to oscillate.

6. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to substantially one-half the velocity of light, a Wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity on the fully accelerated electrons, whereby said waves gain energy through inter-action with the accelerated electrons and any random disturbance is amplified to an electromagnetic wave of substantial amplitude, and an output connection coupled to said wave guide for utilizing a portion of such amplified waves.

7. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode Within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to substantially one-half the velocity of light, a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully-accelerated electrons, an input connection coupled to said wave guide for transmitting thereto electromagnetic waves which travel around the wave guide and are amplified by emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to substantially one-half the velocity of light, a wave guide structure around the periphery of said orbital paths for transmitting electromagnetic waves at substantially the same angular velocity as the fully-accelferated electrons, an input connection coupled to said wave guide for transmitting thereto electromagnetic waves Qwhich travel aboutthe waveguide and are amplified by ction withthe accelerated electrons, anoutput con- .nectloncoupled to said ,wave guide for utilizing a'portion iof suchamplified waves, and an attenuator coupled to i said wave guide for suppressing the: inherent tendency of .the apparatus to oscillate. V i V 9L Microwave apparatus; comprising .an evacuated structureincluding a plurality of hollow electrodes form- Sing a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode-within said'circular space, means toprovide a agneticflfield through 'said space whereby the electrons emitted by said cathode travel in orbital paths about the jcathodeand'repeatedly traverse said gap, means to apply alternadng'voltage across said gap whereby said electrons are accelerated to high velocities, an annular hollow wave @guide having an inner. wall irnmediatelysurrounding said circular space, said inner wall having a plurality of slots connecting said wave guide to said circular space, an 5' output connection, and means coupling said'o utput con- 'nection to said wave guide. V. V

A microwave oscillator comprising an evacuated structure including a plurality of hollow electrodes forming a substantially: circular evacuated space, said hollow electrodeshbein'g separated by a gap, an electron-emitting cathodewithin said circular space,.means to provide a magneticficld through 'said space whereby the electrons emitted bysaid cathode travel in orbital paths about the cathode and repeatedly traverse said gap, a plurality of 1 resonant chamberslconnected to each. end of said gap, 1' means to supplyelectromagnetic energy to at least one of said resonant chambers, whereby an alternating voltage is'applied acrosssaid gap which accelerates said electrons to high velocities, an annular hollow wave guide having a .plurality of slotsin'said inner wall connecting said wave guide to said circular space, an output connection, and means coupling said-output connection to said wave guide. 7 11. A .rnicrowave amplifier. comprising an evacuated structureincluding a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes beingseparated by a gap, an electron-emitting cathode within said circular space, n eansrtoprovide a. magnetic field through said space whereby the electrons emitted by said cathodetravel in orbital paths aboutthe cathode and. repeatedly'traverse said gap, a plurality of resonant chambers connected to respective ends of'said gap,.means. to supply electromagnetic energy to at, least one of said resonant chambers whereby. an alternating electrons to high velocities, an annular hollow wave guide ,1 having an inner, wall immediately, surrounding said vcirw cular space,a plurality of slots in said inner wall connecting said Wave guideto saidcircularspace, input and outmaterial-within said Wave guide to suppress the inherent tendency of said apparatus to oscillate. i V I 7 112. A microwav e amplifier comprising an evacuated structure including a plurality of hollow electrodes formelectrodes being separated by a gap, anelectron-emitting V cathode within said circular space, means to provide a magnetic fieldthrough said spacey/hereby the electrons cathodeand repeatedly traversesaid gap, means to apply alternating voltage :across said gap whereby said electrons are. accelerated to high velocities, a plurality of resonant cavities arranged around the periphery of said circular space and connected thereto, a hollow annular wave guide having an inner wall immediately surroundingsaid' cavi-' ties, s'aidinner wall haying a plurality of slots connectingsaid wave guide and said cavities, said annular wave guide an inner wallirnmediately surrounding said circular space,

' voltage'is provided across said gap which acceleratessaid i put connections, means couplipg saidinput andoutput connections to said wave guide, and an attenuator of lossy ing a substantially circular evacuated space, said hollow.

emitted by said cathode travel'in orbital paths about the having a radius substantially twice as large as the radius of'said circular space, an. output conncctiomand means coupling saidoutput connection to said wave guide.

l3. Microwave apparatus .comprising' an evacuated structure including a'plurality o ffhollow'electrodes form ing a substantially circular evacuated space, said hollow V electrodes being separated by a gap, an electron-emitting cathode within said circular space, means to provid a magnetic field. through said space whereby the electrons emitted by said cathode'travel in orbital paths about the cathode .andlrcpeatedly traverse said gap, means to apply alternating voltage across said gap wherebysaid electrons ing a substantially 'circularrevacuated space, said hollow V electrodes being separated by a gap, an electron-emitting cathodewithin said circular space, means to provide a magnetic field through said space. whereby the electrons emitted by said cathode travel in orbital paths about. the cathode-and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby. said electrons are accelerated to high velocities,' a-wave guide structure comprising a circular ring of dielectricmaterial immedi: ately surroundingdsaid circular space, and an output connection coupled to said waveguide, 7

15. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuatedspace, 'said hollow electrodes being separated by a gap, an electron-emitting cathode. within said circular space, means, toprovide a magnetic field through said space whereby the electrons emitted by, said cathode travel in orbital paths about. the cathode and repeatedly traverse said gap, means to apply alternating voltage across saidgap whereby saidrelectrons' V are accelerated to high velocities, a wave, guide structure comprising a circular ring of dielectric material immediately surrounding said circular space, input' and output connections coupled 'to said wave guide structure, and. an attenuator, coupled to said wave guide structure to suppress the inherent tendency of the apparatus to oscillate;

'l6..A microwave amplifier comprising .an evacuated ttructure including a plurality of hollow electrodes form'a ing a substantially circular evacuated space, said hollow electrodes-being separatedby a gap, an electron-emitting cathode within said circular space,gmeans to provide .a

.magnetic field through saidspace whereby the electrons emitted .by said cathode travel in orbital paths 'aboutthe.

cathode and repeaxdlytraverse said gap, means to apply alternating voltage across saidgap whereby said electrons are accelerated to 'hightvelocities, a wave guide-structure comprising a circular ring of'dielectricmaterial immedi-l ately surrounding said circular space, input and output connections coupled'to said wave guide structure, and-a thin film of electrically conductive material coated upon electrodes being separated'by a gap, an electron-emitting cathode Within said circular space, means to provide a magnetic field through said space whereby the; electrons emitted by'said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, meansto-apply alternating voltage across said gap whereby said electrons are accelerated to highvelocities, and a wave guide structure' comprising an annularchelix ing said circular'spacec r immediately surround- '18. A' microwaveoscillator comprising-an evacuated structure including a plurality of hollow electrodes form ing a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron emitting 5 cathode within said circular spaceyrneans to provide a evacuated magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, a wave guide structure comprising an annular helix immediately surrounding said circular space, and an output connection coupled to said wave guide structure.

19. A microwave amplifier comprising an evacuated structure including a plurality of hollow electrodes forming a substantially circular evacuated space, said hollow electrodes being separated by a gap, an electron-emitting cathode within said circular space, means to provide a magnetic field through said space whereby the electrons emitted by said cathode travel in orbital paths about the cathode and repeatedly traverse said gap, means to apply alternating voltage across said gap whereby said electrons are accelerated to high velocities, a wave guide structure comprising an annular helix immediately surrounding said circular space, and input and output connections respectively coupled to said wave guide structure.

References Cited in the file of this patent UNITED STATES PATENTS 

